.calculator {
    width: 200px;
    margin: 0 auto;
    padding: 10px;
    background-color: #f1f1f1;
    border: 1px solid #ccc;
  }
  
  #display {
    width: 100%;
    margin-bottom: 10px;
    padding: 5px;
  }
  
  .keypad {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    grid-gap: 5px;
  }
  
  button {
    padding: 10px;
    font-size: 18px;
  }